Phenotypic plasticity accounts for changes in plant phosphorus-acquisition strategies from mining to scavenging along a gradient of soil phosphorus availability in South American Campos grasslands

Plants have evolved numerous traits to acquire phosphorus (P). Correspondingly, soil P availability modulates the functional composition of many plant communities. However, it is unclear to what extent plant species modulate the expression of different P-acquisition strategies (phenotypic plasticity). Moreover, how variation in soil-P availability interacts with plant phenotypic plasticity and species turnover to determine what P-acquisition strategies are present in highly diverse communities? To address these questions, we assessed associations between plant-available soil P and the magnitude of several P-acquisition traits in both individual species and plant communities in Campos grasslands. Root phosphatase activity (phosphomonoesterase and phosphodiesterase), leaf manganese (Mn) concentration (a proxy for carboxylate concentration in the rhizosphere) and arbuscular mycorrhizal (AM) colonization were assessed in 105, 52 and 54 native plant species, respectively, sampled across three to seven plant communities with contrasting concentrations of plant-available soil P. Furthermore, root diameter and plant cover of those species were also quantified. Variation in P-acquisition strategies among species was large: 157- and 118-fold for phosphatases, 96-fold for leaf [Mn] and 39-fold for AM colonization. Between half and two-thirds of the variation in community-weighted mean P-acquisition traits was accounted for by the interactive factors plant-available soil P, soil pH and root diameter. At low-P availability, phosphatases and carboxylate exudation (P-mining traits) and thin roots predominated, particularly at low soil pH. At higher P availability, AM associations (P-scavenging trait) and thicker roots were more common. Synthesis. Phenotypic plasticity was a major source of variation in the response of P-acquisition traits to soil properties, particularly for P-mining traits. Our results reveal that the plasticity of the expression of plant P-acquisition strategies in individual species was more important than changes in species presence or cover as a mechanism underlying shifts between P-mining and P-scavenging strategies as plant P availability varied across communities.